Froth flotation process

ABSTRACT

941,348. Froth flotation. HEYL &amp; PATTERSON Inc. Dec. 4, 1961 [April 18, 1961], No. 43241/61. Heading B2H. A froth flotation process comprises the steps of progressively advancing slurry along on elongated receptacle 2, impelling into the slurry below its surface at intervals along its path e.g. through chambers 10, agitating liquid and gas causing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from the receptacle, at least part of the withdrawn slurry being re-impelled into the slurry and thus recirculated to constitute at least part of the agitating liquid, and delivering a tail&#39;s fraction at the end of the path. The receptacle is divided into four cells A, B, C, D by baffles 4, 5, 6. The slurry is fed in under a baffle 3 and it gradually progresses to a tails outlet 9 by way of baffles 7, 8. The chamber 10 in each cell is fed with slurry from a pump 17 tangentially through a conduit 11 so that the slurry swirls out of an outlet 12, mixes with air from a pipe 13 and distributes itself throughout the particular cell. Each cell has a pipe 18, 19, 20, or 21 with a control valve 18&lt;SP&gt;1&lt;/SP&gt;, 19&lt;SP&gt;1&lt;/SP&gt;, 20&lt;SP&gt;1&lt;/SP&gt; or 21&lt;SP&gt;1&lt;/SP&gt; respectively through which slurry maybe withdrawn to feed the pump 17. It has been found that the best results are obtained if the feed for the pump is taken from the cell C or the cell D, or from the outlet 9, which is in effect the same as taking it from the cell D. The baffles 4, 5, 6 may be dispensed with and in some cases the slurry withdrawn from the receptacle 2 may not form all the agitating liquid, or only part of the slurry withdrawn may be used for agitation.

Filed April 18, 1961 Fmncg td firor WZy P2 .p VN

United States Patent 3,048,272 FROTH FLOTATION PROCESS Francis G. Miller, Monroeville, Pa., assignor to Heyl 8: Patterson, lnc., Pennsylvania Filed Apr. 18, 1961, Ser. No. 76,516 12 Claims. (Cl. 209-466) This invention relates to a froth flotation process and particularly such a process in which agitation and froth formation are accomplished by irnpelling into the slurry below the surface of the slurry agitating liquid and gas. The-invention further relates -to such a process in which agitating liquid and gas causing agitation and froth formation are impelled into the slurry below the surface of the slurry at intervals along its path. The invention still further relates to withdrawal of a portion of the slurry and utilization of at least part of the withdrawn slurry to constitute at least part of the agitating liquid. The invention still further relates to withdrawing of such portion of the slurry at a particular portion or zone of the froth flotation process whereby advantages presently to be described are obtained.

In copending applications Serial Nos. 44,082, filed July 20, 1960, now abandoned, and 60,661, filed October 5, 1960, there are disclosed aeration process which are adapted to froth flotation and which when so adapted involve impelling into a slurry below the surface of the slurry agi tating liquid and gas. Such impelling into the slurry below the surface of the slurry of agitating liquid and gas causes agitation and froth formation. The prior method of accomplishing agitation was by a driven impeller submerged in the slurry. The improvement of said copendiug applications makes for greatly increased efficiency and reduction of cost since no driven impeller is needed and the agitation and froth formation occur as an incident to the impelling of the liquid and gas into the slurry.

I have conceived that further important advantages in economy and efficiency can be realized by utilization of aerating processes of the general type disclosed in said copending applications in a froth flotation process which comprises progressively advancing slurry generally along a predetermined path. I impel into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation; and 1 preferably withdraw a portion of the slurry from said path and utilize at least part of the withdrawn slurry to constitute at least part of the agitating liquid.

I find that there is an especial advantage in withdrawing the slurry which is to constitute at least part of the agitating liquid from the portion of the path of the slurry in the froth flotation process at which one-half of the slurry is disposed measuring countercurrent from the terminus of the path toward which the slurry advances. I prefer to withdraw such slurry from the portion of the path of the slurry in the froth flotation process at which the third onefourth of the slurry is disposed measuring in the direction of current flow from the terminus of the path from which the slurry advances.

The withdrawn slurry may constitute less than all of the agitating liquid, or less than all of the withdrawn slurry may constitute the agitating liquid, although normally the withdrawn slurry without diminution or dilution constitutes the agitating liquid or agitating slurry. New slurry is introduced through the feed at the feed end of the flotation process and the froth carrying with it particles removed from the slurry is skimmed off, overflowed or otherwise removed as known to those skilled in the art.

In one aspect of the invention I prefer to withdraw the slurry which is to constitute the agitating liquid from the portion of the path of the slurry through the flotation process at the side of an imaginary vertical plane bisecting Pittsburgh, Pa., a corporation of Patented Aug. 7, 1962 the slurry in said path into generally equal volumes which faces toward the terminus of said path toward which the slurry advances. In certain processes it may be desired to withdraw the slury which is to constitute the agitating liquid from the terminus of the path of the slurry through the flotation process toward which the slurry advances, i.e., the so-called tails of the froth flotation process.

In one somewhat more specific aspect of the invention I provide a froth flotation process comprising progressively advancing slurry generally along a continuous path in an elongated receptacle and impelling into the slurry below thesurface of the slurry at intervals along the length of the receptacle agitating liquid and gas causing agitation and froth formation, and I preferably withdraw a portion of the slurry from the receptacle and utilize at least part of the withdrawn slurry to constitute at least part of the aforementioned agitating liquid. Alternatively my froth flotation process may comprise progressively advancing slurry successively through a. series of cells and impelling into the slurry below the surface of the slurry in each cell agitating liquid and gas causing agitation and froth formation, and I preferably withdraw a portion of the slurry from at least one of the cells and utilize at least part of the withdrawn slurry to constitute at least part of the agitating liquid. Preferably the slurry which is to constitute the agitating liquid is withdrawn from one of the cells which is at least as close to the delivery end of the series of cells as to the feed end thereof. In a preferred process the series of cells constitutes at least three cells and the slurry which is to constitute the agitating liquid is withdrawn from at least one of the last two cells of the series at the delivery end thereof. In some cases the slurry which is to constitute the agitating liquid maybe constituted wholly or in part by the tails.

Other details, objects and advantages of the invention will become apparent as the following description of certain present preferred methods of; practicin the same proceeds.

In the accompanying drawingl have illustrated diagrammatically a present preferred method of practicing the invention and one form of apparatus which may be employed in practicing the invention.

Referring now more particularly to the drawing, there is shown diagrammatically a froth flotation apparatus in which slurry advances progressively from left to right. The apparatus is shown as comprising an elongated receptacle designated generally by reference numeral 2, the receptacle 2 being shown as being diw'ded into four cells designated respectively by the letters A, B, C and D. The feed slurry enters the apparatus at the point indicated by the arrow marked Feed. It flows beneath a downwardly reaching baffle 3 into cell A, thence over an upwardly reaching bafiie 4 into cell B, thence over an upwardly reaching haflle 5 into cell C, thence over an upwardly reaching baths 6 into cell D and thence under a damn wardly reaching bafile 7 and over an upwardly reaching baflie 8 to a tails discharge outlet 9 indicated by the arrow marked 'lails. It is possible to accomplish satisfactory results without using the baffles 4, 5 and 6, in which case the slurry advances through an elongated unbafiled recep tacle, but for purposes of explanation and illustration I shall consider that the battles 4, 5 and 6 will be employed whereby the receptacle 2 is divided into the cells A, B, C and D.

In a froth flotation process the froth is formed by agitating the slurry and passing finely divided gas therethrough, the bubbles of gas rising through the slurry and picking up certain particles therein while other particles are not picked up by the bubbles and remain in suspension in the apparatus and are ultimately discharged as tails. While various gases may be employed the one most commonly used is air and for purposes of explanation and illustration the gas utilized in froth formation will be deemed to be air. The slurry contains the two classes of particles above mentioned and also, if indicated, a substance which may be selected from a group of substances we l known to those skilled in the froth flotation art and per se forming no part of the present invention causing or helping to cause selected particles in the slurry to be carried up by the air bubbles and other particles to gravitate and pass out as tails.

One use to which my invention may be put is in the cleaning of finely pulverized coal, i.e., the separation of the particles of coal from the particles of foreign matter intermingled therewith. For present purposes the slurry will be deemed to be composed of water carrying particles of coal and foreign matter and a suitable substance known to those skilled in the art causing or helping to cause the particles of coal to be picked up by the rising air bubbles so as to become a part of the froth while the particles of foreign matter are not picked up by the bubbles and remain in suspension and pass out as tails. The froth is separated from the remaining slurry in any suitable mannet as known to those skilled in the art. as, for example, by flowing over the tops of the receptacle walls or being skimmed off or otherwise removed.

I agitate the slurry by impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation. The means for impelling the agitating liquid and gas into the slurry below the surface of the slurry may be means such as are disclosed in the aforementioned applications Serial Nos. 44.802 and 60,661. For example, I may provide at intervals along the path of the slurry. and in each cell when the slurry passes successively through cells, a cylindrical chamber into which the agitating liquid or slurry is delivered generally tangentially through an inlet conduit 11. the agitating liquid swirling and passing downwardly and into the slurry in the receptacle or cell through an outlet 12 where it spreads and distributes itself in the body of slurry in the receptacle or cell. The air may be introduced in any suitable manner such as through a pipe 13 which may be coaxial with the outlet 12 and disposed to deliver the air upwardly so that it is intimately associated with the agitating liquid or slurry and is broken up thereby in to fine bubbles which rise through the body of slurry. as shown, for example, in FIG. 5 of application Serial No. 60,661. The air may be supplied under pressure through a header 14 which delivers it to a series of the pipes 13. there being one pipe 13 for each agitating liquid outlet 12. As shown in the drawing, when the apparatus is divided into cells agitating liquid and air will be introduced into each cell. When an elongated receptacle not divided into cells is utilized agitating liquid and air will be intgoduced into the slurry at intervals along the path of the s urry.

The agitating liquid is delivered to each of the inlet conduits 11 through a pipe 15. The pipes 15 are fed by a header 16 through which agitating liquid is pumped by a pump 17. The agitating liquid is preferably consututed at least in part by slurry withdrawn from the flotation process. I preferably withdraw slurry from the bottom of the receptacle or cell or cells and recirculate the withdrawn slurry as agitating liquid. While I prefer to recirculate all of the withdrawn slurry as agitating liquid without diminution and without dilution I may in certain instances. if found desirable. utilize only a portion of the withdrawn slurry for recirculation as agitating liquid or I may add other liquid to all or a portion of the withdrawn slurry to constitute the agitating liquid.

The recirculating of withdrawn slurry as gitating liquid impelled into the slurry below the surface of the slurry at intervals along its path affords remarkable elliciency. I have found that it is preferable to withdraw the slurry which is to be recirculated as agitating liquid from the portion of the path of the slurry in the froth flotation process at-which one-half of the slurry is disposed measuring countercurrent from the terminus of the path toward which the slurry advances. As above indicated. I prefer to withdraw such slurry from the portion of the path of the slurry in the froth flotation process at which the third one-fourth of the slurry is disposed measuring in the direction of current flow from the terminus of the path front which the slurry advances. Also, as above indicated, I prefer to withdraw the slurry which is to constitute the agitating liquid from the portion of the path of the slurry through the flotation process at the side of an imaginary vertical plane biseeting the slurry in said path into generally equal volumes which faces toward the terminus of said path toward which the slurry advances. When the froth flotation process is carried out using cells through which the slurry progressively advances I prefer to withdraw the slurry which is to be recirculated as agitating liquid from one of the cells which is at least as close to the delivery end of the series of cells as to the feed end thereof.

In the drawing I show pipes 18, 19, 20 and 21 for withdrawing slurry from the bottoms of the cells A, B, C and D respectively. The pipes 18, 19, 20 and 21 deliver the withdrawn slurry to a header 22 which feeds the pump 17. A valve 18 is disposed in the pipe 18, a valve 19 is disposed in the pipe 19. a valve 20' is disposed in the pipe 20 and a valve 21 is disposed in the pipe 21. Thus it will be seen that by selective opening and closing of the valves 18. 19', 20' and 21 the operator may predctcrmine from which cell or cells. or, in the case when a single elongated receptacle not divided into cells is employed, from which portion or portions of the path of advance of the slurry, the slurry which is to constitute the agitating liquid is with drawn. Actually the apparatus shown diagrammatically in the drawing is an experimental apparatus constructed to establish my thesis as to the most desirable location from which to withdraw the slurry which is to constitute the agitating liquid. I operate the process by withdrawing slurry from each of cells A, B, C and D in turn to determine the relative efliciency of the process in each case. I find that optimum results are obtained when the slurry which is to be recirculated as agitating liquid is Withdrawn from cell C.

To illustrate, let it be assumed that each of cells A. B, C and D contains 600 gallons of slurry. The efliciency of a froth flotation process is related to retention time. i.e., the time during which the slurry is retained in intimate association with the air bubbles producing the froth. In order to have an overall retention time in each cell (cell volume divided by cell feed where the feed is expressed in gallons per minute and cell volume is expressed in gallons) of three minutes when using four cells. a volume of 800 gallons per minute must flow to the froth flotation unit which includes the four cells. If a volume per minute equal to one-third the volume of the cell is supplied to each cell as agitating liquid then with 800 gallons per minute feed and four fitlO-gallon cells it is necessary to circulate 800 gallons per minute to the four cells, each cell receiving 200 gallons per minute.

In a system of this kind the possibility exists that some material will reach the tails discharge without having the benefit of the entire three minutes of treatment while on the other hand some material will stay in the unit longer than three minutes. I have found that the place along the flotation unit from which the agitation liquid or slurry is taken has an important effect on the minimum retention time. i.e., the minimum time that any particle remains in the flotation unit for treatment.

Initially I opened the valve 18 and closed the valves 19. 20' and 21' so that the agitation slurry was taken from cell A. In such case the flow into cell A is 800 g.p.m. (gallons per minute)+200 g.p.m. 800 g.p.m. leave cell A by way of the pump 17 to be used for agitation and 200 g.p.m. flow to cell B. That 200 g.p.m. plus the 200 g.p.m. entering cell B as agitating slurry provide a feed to cell B of 400 g.p.m. The feed to cell C will be 400 g.p.m.-l-ZOO g.p.m. or 600 g.p.m., while the feed to cell D will be 600 g.p.m.+200 g.p.m. or 800 g.p.m. The retention time in each cell is calculated by dividing the cell volume by feed volume per minute to the cell. The retention time in the respective'cells with the valve 18' open and the valves 19, 20 and 21' closed is as follows:

800 gaL/miii. Minimum retention time='1.35 minutes In arriving at the minimum retention time, the retention time in cells B and C must be excluded because material which travels to cell D by way of the pump 17 as agitating slurry does not get the benefit of cell B or cell C. Therefore the minimum retention time in the unit with the valve 18 open and the valves 19', 20'. and 21' closed is .60 minute in cell A plus .75 minute in cell D or a total of 1.35 minutes.

I next opened the valve 19' and closed the valves 18', 20 and 21' so that the agitating slurry was taken from cell B. In such case cell A receives 800 g.p.m.+200 g.p.m., cell 13 receives 1,000 g.p.rn.+200 g.p.m. while 800 g.p.m.leave cell B by way of pump 17 as agitating slurry. Cell C receives 400 g.p.m.+200 g.p.rn. and cell D receives 600 g.p.m.+200 g.p.m. The retention time in the respective cells with the valve 19' open and the valves 18', 20 and 21' closed is as follows:

00 galT/ii i 1i W 7 Minimum retention tirne LSli minutes In arriving at the minimum retention time the retention time in cell C must be excluded because material which travels to cell D by way of the pump 17 as agitation slurry does not get the benefit of cell Ci Therefore the mini mum retention'tirne in the unit with the valve 19 open and the valves 18', 20 and 2t closed is .60 minute in cell A plus .50 minute in cell B plus .75 minute in cell D or a total of 1,85 minutes.

I next opened the valve 20' and closed the valves 18, 19' and 21' so that the agitating slurry was taken from cell C. In such case cell A receives 800 g.p.m.+200 g.p.m,, cell 8 receives 1,000 g.p.rn.+200 g.p.m. and cell C receives 1,200 g.p.m.+200 g.p.m., while 800 g.p.m. leave cell C by way of pump 17 as agitating slurry. Cell I) receives 600 grant-+200 g.p.m. None of the cells is bypassed. The retention time in the respective cells with the valve 20' open and the valves 18, 19 and 21 closed is as follows:

800 gal. /hnn. Minimum retention timc==2.28 minutes In this case all of the material receives the benefit of all of the cells so the minimum retention time is the total of the retention times in the respective cells.

I next opened the valve 21 and closed the valves 18', A 19' and 20 so that the agitating slurry was taken from.

In such case cell A receives 800 g.p.m.+200

cell D. g.p.m., cell B receives 1,000 g.p.m.+200 g.p.m., cell C receives 1,200 g.p.m.+200 g.p.m. and cell Dreceives 1,400 g.p.m.+200 g.p.m., while 800 g.p.m. leaves cell D by way of pump 17 as agitating slurry. Again none of the cells is bypassed. Theretention time in the respective cells with the valve 21 open and the valves 18', 19' and 20' closed is as follows:

600 gal Cell v minute 1 600 gal. (-el. 13 Tim o.s0 minute 600 gal. Cell C -QQ minute our D 600 =0.38 rhinute T000 gaL/min. Minimum retention tirne= 1.91 minutes In this case the minimum retention time is substantially greater than when the agitation slurry is withdrawn from cell A or from cell B but somewhat less than when the agitation slurry is withdrawn from cell C.

Therefore in a flotation unit such as that shown in the drawing I prefer to withdraw the agitation slurry from cell C although good results are obtained by withdrawing it from cell D. Incidentally the agitation slurry may be withdrawn from the tails outlet 9 instead of from cell D with the same result as though it were withdrawn from cell D.

.Agitating liquid from an outside source may be in troduced into the header 22 through a. pipe 23, and liquid may be withdrawn from the header 16; through a pipe 24.,

While I have illustrated and described a present preferred method of. practicing the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously practiced within the scope of the following claims.

I claim:

l. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through operatively parallel conduits into the slurry, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of said path. I

2. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry be ing recirculated to constitute at least part of the aforementioned agitating liquid, the withdrawn slurry being withdrawn from the portion of said path at which onehalf of the slurry is disposed measuring countercurrent from the terminus of the path toward which the slurry advances, and delivering a tails fraction at the end of said path.

3. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas caus ing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, the withdrawn slurry being withdrawn from the portion of said path at which the third one-fourth of the slurry is disposed measuring in the direction of current flow from the terminus of the path from which the slurry advances, and delivering a tails fraction at the end of said path.

4. A froth fiotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through operatively parallel conduits into the slurry, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, with withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of said path.

5. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through operatively parallel conduits into the slurry, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry being recirculated to constitute the aforementioned agitating liquid, and delivering a tails fraction at the end of said path.

6. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through opera tively parallel conduits into the slurry. separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, the withdrawn slurry being recirculated to constitute the aforementioned agitating liquid, and delivering a tails fraction at the end of said path.

7. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas caus ing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry being recirculated to constitute at least part of the afore mentioned agitating liquid, the withdrawn slurry being withdrawn from the portion of said path at the side of an imaginary vertical plane biscctiug the slurry in said path into generally equal volumes which faces toward the terminus of said path toward which the slurry advangrcs, and delivering a tails fraction at the end of said pat 8. A froth flotation process comprising progressively advancing slurry generally along a predetermined path, impelling into the slurry below the surface of the slurry at intervals along its path agitating liquid and gas cause ing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from said path, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, the withdrawn slurry being withdrawn from the terminus of said path toward which the slurry advances, and delivering a tails fraction at the end of said path.

9. A froth flotation process comprising progressively advancing slurry generally along a continuous path in an elongated receptacle, impelling into the slurry below the surface of the slurry at intervals along the length of the receptacle agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through operatively parallel conduits into the slurry, separating froth from the slurry, withdrawing a portion of the remaining slurry from the receptacle, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of said path.

10. A froth flotation process comprising progressively advancing slurry successively through a series of cells,

impelling into the slurry below the surface of the slurry in each cell agitating liquid and gas causing agitation and froth formation, the agitating liquid being delivered from a common source through operatively parallel conduits into the slurry, separating froth from the slurry, withdrawing a portion of the remaining slurry from at least one of the cells, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of the series of cells.

11. A froth flotation process comprising progressively advancing slurry successively through a series of cells, impelling into the slurry below the surface of the slurry in each cell agitating liquid and g s causing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from one of the cells which is at least as close to the delivery end of said series of cells as to the feed end thereof, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of the series of cells.

12. A froth flotation process comprising progressively advancing slurry successively through a series of at least three cells, impelling into the slurry below the surface of the slurry in each cell agitating liquid and gas causing agitation and froth formation, separating froth from the slurry, withdrawing a portion of the remaining slurry from at. least one of the last two cells of said series at the delivery end thereof, at least part of the withdrawn slurry being recirculated to constitute at least part of the aforementioned agitating liquid, and delivering a tails fraction at the end of the series of cells.

References Cited in the file of this patent UNITED STATES PATENTS 1,374,500 Greenawalt Apr. 12, 1921 2,416,066 Phelps Feb. 18, 1947 2,778,499 Chamberlin m.-- Jan. 22, 1957 2,931,502 Schoelcl ............,..,...,....m... Apr. .5, 1960 

